In a recordable disc, data can be additionally written in units of sessions (each session is a set of a lead-in area including TOC “Table Of Contents” information, a program area containing a data track or an audio track, and a lead-out area showing an end of each session).
In general, when file information is recorded into a disc, a file system including a file and file information is written for every session. In contrast, in a recordable disc, file information is additionally written with the file system in the final data session being linked to files systems which have been recorded before the additional writing, and reading of only the file system in the final session makes it possible to recognize the files in all the linked sessions (linked multisession).
In a general file-based disc playback apparatus, reading of the file system recorded into the final session makes it possible to also play back a file recorded into another session on a linked-multisession disc as mentioned above.
In contrast with this, a method of, when writing additional information, recording the additional information by intentionally not providing a link to a file system recorded before the additional writing to overwrite the additional information (multivolume multisession) can be selected.
Because the file system in the final data session is not linked to any of the file systems in other sessions on a multivolume multisession disc, files which such a general file-based disc playback apparatus as mentioned above can play back are only the file in the final data session.
Conventionally, as methods related to a method of playing back a recordable disc, there have been proposed a method of playing back compressed data recorded into a recordable disc having multiple sessions, and a method of managing musical piece files recorded into a recordable medium in units of sessions, and automatically playing back musical pieces from the musical piece of the musical piece file in the newest session (refer to, for example, patent references 1 and 2).    [Patent reference 1] JP,2003-257023,A    [Patent reference 2] JP,2002-222585,A
In general, a link at a time of additionally writing file information in a recordable disc is provided according to the user's intention, there may be a case in which the file information is additionally written in the recordable disc without being linked with any file system due to the user's misoperation or the like at the time of the additional writing. In this case, it's so inconvenient that any general file-based disc playback apparatus cannot identify any file which has been recorded before the additional writing is performed and therefore cannot play back such a file.
A further problem is that in order to play back a file in a non-linked session, file systems in all the sessions must be checked and therefore it takes much time to carry out a file system reading operation.
Furthermore, a problem with above-mentioned patent reference 1 is that among this time required to carry out a file system reading operation, a time required to start a playback of the file is shortened by checking a file system which exists in the first session on a priority basis and then starting the playback, and then checking a file system which exists in another session after starting the playback, though the leading file included in the first session is not necessarily the desired leading file and the order in which musical pieces are played back differs from that in the normal playback mode.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a file-based recordable disc playback apparatus for and a file-based recordable disc playback method of being able to detect all files recorded into a disc in a short time while keeping the number of times of file system reading operation to a minimum.